Introduction

The disposal of ‘waste’ vapours in the atmosphere is a concern of the chemical industry. Technical solutions for vapour emission control which are economical acceptable are not always available.

When dealing with liquefied gasses in a tank, a considerable part of the total product quantity exist as vapour. Moreover, after discharging the liquid phase from the tank, the tank volume will entirely consist of remaining cargo vapours.

In many cases, facilities for handling these vapour phases are not available, with a consequence that often for one or another reason they are to be realised to a vent stack or a flare system. This spillage of valuable product is coming extreme in case where storage tanks or cargo containment systems are to be gas freed for reasons of cargo change over or internal inspection.

The handling of liquefied gasses and other volatile cargoes often requires a release of product directly in the atmosphere or a release of product to a flare system. The quantities of VOC’s and / or toxic products released in the atmosphere are during change over from one cargo to another one for which a gas freeing of the cargo containment system is required.

Up to 1 pct of the total quantity of product is lost in the atmosphere during cooling, change-over andcleaning of gas storage vessels. Annual emission from world gas tanker fleet only above 275.000 MT (Figures published by SIGTTO)